The present invention pertains to a method of mounting a nipple on a flexible tubular pipe end and also, to a connector comprising said tubular pipe end and the nipple mounted according to the method.
The flexible tubular pipes concerned are better known as “RTPs” (for Reinforced Thermoplastic Pipes) and they are used for land-based (or “on-shore”) applications for transporting hydrocarbons or water under pressure. They have the advantage of being faster to install and more resistant to corrosion than rigid steel pipes. Their inner diameter is relatively small, lying for example between 50 and 200 mm, and the transported fluid is at a pressure generally lying between 50 and 200 bar and at a temperature which may reach as much as 80° C.
The structure of these pipes is relatively simple and inexpensive. They comprise from the inside to the outside an inner polymeric tube made of polymer, an armor generally made of composite materials and an outer polymeric sheath. The inner polymeric tube has a leaktightness function in relation to the fluid transported by the pipe. It is generally made of high-density polyethylene. The function of the outer polymeric sheath, which is in particular made of polyethylene, is to protect the armor.
The function of the armor is to take up the mechanical loads, in particular those related to the pressure of the transported fluid. The armor generally consists of at least one pair of crossed plies of helically wound threads. The two overlaid plies constituting each pair of plies are oppositely wound with helix angles that are substantially equal in absolute value, so as to balance the structure in torsion. This helix angle is advantageously of the order of 55°, so as to take up the axial tensile loads and also the radial loads related to the pressure of the fluid. In most cases, the armor comprises only two overlaid layers, namely a pair of crossed plies of armor threads wound at 55°. When the diameter of the pipe and the service pressure are high, it may be necessary and advantageous to add a second pair of crossed plies of armor threads, so that the armor then comprises four overlaid layers. The threads of the armor plies consist for example of fibers of aramid, carbon, glass or polyester.
The document FR2828722 describes an exemplary “RTP” pipe in which the armor threads are textile strips strengthened with Kevlar® fibers. The document WO2004/068016 presents another example in which the armor threads consist of glass fibers.
The pipes to which the present invention is pertinent are said to be of unbonded type since their various constituent layers are substantially free to slip with respect to one another when the pipe is flexed.
One of the drawbacks of these pipes is the cost of their connection. Indeed, in order to be connected these pipes are equipped at their end with a nipple, and the costs of this nipple added to the costs of mounting are relatively significant by comparison with the cost of the bare pipes.
A method of mounting a nipple at the end of a flexible tubular pipe so as to produce a connector is for example described in the document FR 2 754 585. The nipple comprises a connection end and, opposite therefrom, a mounting end intended to be fitted into the end of said pipe. Said connector also comprises a sleeve which shrouds the pipe end so as to clamp the tubular pipe end onto said mounting end. Accordingly, the inner diameter of the mounting end is deformed and increased by force by implementing a technique dubbed tube expansion, said technique consisting in forcibly introducing and displacing a tube expander inside and along said mounting end, said tube expander having an outside diameter greater than the initial inside diameter of said mounting end. The effect of this operation is to compress the walls of the end of the pipe inside the sleeve. Thereafter, in order to perfect this mounting, the outer diameter of the sleeve is deformed and reduced by force by implementing a drawing technique. This results in a tightening or clamping of the end of the pipe between on the one hand the mounting end of the nipple and on the other the sleeve, said clamping ensuring the functions of mechanical joining and leaktightness. This solution exhibits the drawback of requiring relatively sizeable and expensive specialized tooling to carry out the tube-expansion and drawing operations. Moreover, it is necessary to provide for a relatively sizeable length of pipe end held tight between the sleeve and the nipple so that, under extreme conditions, the nipple does not become detached from the end of the pipe. Consequently, the cost of the materials used to produce the nipple is correspondingly increased.